The present disclosure relates to a method for operating a machine, in particular a wave energy converter, located in choppy waters, for converting energy from a wave movement of a fluid into another form of energy, a computing unit for carrying out said method and a correspondingly operated wave energy converter.
Wave power plants (wave energy converters) utilize the energy from sea waves to acquire electric current. Relatively new design approaches use rotating units here which convert the wave movement into a torque. In said units, inter alia hydro-dynamic floating bodies, (i.e. bodies which generate lift when there is a flow around them) are used as coupling bodies by means of which a lift moment is generated from the incoming wave, which lift moment can be converted into a rotational movement of a rotor. The corresponding coupling bodies are arranged, for example, on a crank drive. Lift forces are produced at the coupling bodies by a superimposed incoming flow from the orbital flow of the wave movement and the coupling bodies own rotation, which lift forces cause a torque to be introduced into the crank drive.
The lift of a hydrodynamic lift body can be changed by means of its pitch angle with respect to the medium which is flowing against them, for example air or water. In particular, for such rotating wave power plants with hydrodynamic floating bodies reliable adjustment is important since desynchronization of the rotor from the orbital flow as a result of vortex breakdown can lead to complete decoupling from the shaft.
In particular, owing to the multichromatic wave states of sea waves it is necessary to perform open-loop and/or closed-loop control of a corresponding system in such a way that there is always an optimum flow against the flow bodies and that the flow bodies are operated as close as possible to the conversion optimum. As a result, a maximum energy yield can be achieved. Actuation variables are here, in particular, the generator torque and the adjustment of the pitch angle of the coupling bodies. This results in corresponding angles of flow against the coupling bodies and a phase angle between the rotation of the system and the wave orbital flow.
U.S. Pat. No. 7,686,583 B2 proposes determining an incoming flow angle of a fluid flowing against a coupling body, on the basis of a measured lift in conjunction with the flow speed. For this purpose, different measuring means, including pressure sensors, are provided. On this basis, it is then possible to perform a control which comprises, for example, adjustment or torsion of the coupling bodies in order to adapt them to an oblique incoming flow or a corresponding re-alignment of the total system. However, in particular local differences at a coupling body cannot be detected by the method disclosed in said document. The method also permits no conclusions to be drawn about an imminent or already occurred vortex breakdown.
Therefore, there is still the need for improved possibilities for operating a wave energy converter.